Wideband communication broadcasts, e.g., high definition television ("HDTV") broadcasts, may suffer from narrowband interference signals produced by numerous different sources including, e.g., Citizen Band radio harmonics, HAM radio, land mobile, etc.
In addition, cable television broadcasts may suffer from narrowband interference which results from testing of the cable system during normal operation. For example, known cable television signal testing procedures sweep a narrow tone signal across the cable television system's broadcast frequency spectrum during normal operation to check the transmission quality of the system. To a cable television viewer this narrowband test tone appears as a narrowband interference signal which interferes with television reception.
Accordingly, it is desirable to provide a means of eliminating or reducing narrowband interference signals from wideband communication signals being received by, is e.g., a HDTV receiver or a cable television system to thereby improve reception.
Current techniques used to avoid interference by many HDTV system proponents only address NTSC television signal interference which results from the simulcasting of HDTV signals and NTSC signals in the same frequency spectrum. Such NTSC interference occurs at predictable frequencies. Furthermore, NTSC interference peaks due to NTSC audio carrier, chrominance subcarrier and picture carrier signals being spaced at predictable frequency intervals from each other. Thus, NTSC interference, with its known frequency spacing, lends itself to interference cancellation techniques, such as the use of comb filters having fixed frequency spacing between notches, which are not generally applicable to the removal of narrowband interference signals of unknown frequency and intensity.
The general failure of proposed HDTV systems to address the problem of narrowband signal interference from sources other than NTSC signals, and particularly narrowband interference from sources of unknown frequency, decreases a HDTV receiver's ability to detect, decode, and display HDTV signals in areas where narrowband signal interference from, e.g., a ham radio, is present.
Accordingly, a narrowband interference canceler which can operate without a priori information about an interference signal is needed in order to improve reception of wideband communication signals by removing narrowband interference signals when present.